Goodreads, the largest social network specifically for readers, claims a dual mission: “to get people excited about reading,” and, via their Goodreads Author program, “to help authors reach their target audience — passionate readers.”

The site boasts 3.6 million members who have added more than 100 million books to their virtual shelves and created more than 30,000 groups covering a variety of interests.

“We have 13,000+ authors on the site and many of them want to reach readers directly,” explains Patrick Brown, Goodreads’ Community Manager. “Previously, they could engage, but they couldn’t really make a sale.”

In March, Goodreads quietly began offering eBooks; first, a modest selection of out-of-copyright eBooks supplied by Feedbooks, then allowing authors to upload their own eBooks and, starting in May, enabling them to sell them.

“We roll stuff out and see how it gets used before we make a big deal about it,” says Brown. Despite minimal fanfare, “we found the eBooks were getting quite a bit of traffic. It kept people on Goodreads.”

Sensing an opportunity, “we felt like it was a natural fit to move that experience into the iPhone app.”

The Goodreads iPhone app, which also launched in March, has been downloaded by more than 30,000 readers so far, and was updated yesterday to add an intriguing new feature: an embedded eReader. Fully integrated with the app, the eReader connects to users’ profiles and allows them to add eBooks to their shelves, add notes, and share their progress with their friends. They can also purchase and download eBooks via the mobile site without leaving the app. (NOTE: It also works pretty well on the iPad.)

Goodreads eBooks are in ePUB format, DRM-free, with authors setting the price and getting 70% of the revenue, payable via check or Paypal at any point after they’ve earned $50.

“We wanted to be DRM-free,” says Brown, “and we didn’t feel like we’ve ever seen a customer experience that was really great. The Kindle experience is pretty good but you’re limited to a sort of fake ownership. With our platform, readers can download the eBooks and read them on any device that supports ePUB.”

It’s also an opportunity for authors to convert social networking efforts into direct sales.

“It used to be that you were on the train and would see people reading books, and now you’ll see the same thing happening online,” says Brown. “We’re hoping to be the network that let’s people with a bunch of devices talk to each other.”

Any of the major eReader apps could conceivably use Goodreads’ APIs to add social reading functionality, including new players like Google, Blio and Copia, the latter of which has made “social reading” a core part of its pitch. Brown says SONY currently uses their API only for reviews, and they’ve had meetings with others that could result in similar integration.

As for Goodreads itself, Brown says an iPad app is “#1 on the to-do list,” but it’s not in development yet. Meanwhile, a third-party is developing a Goodreads app for Android, and while there’s some demand from Blackberry users (like me!), there are no plans for an app yet.

While selling eBooks is a nice add-on for their Author program, Brown says their focus remains on reviews, and that the new eReader enhances that experience. In other words, there are no plans to shift from being an online community to an online retailer and start selling print books, too.

“Some of our users might not respond to that well,” says Brown. “There’s always suspicion about Amazon reviews… we want to maintain the integrity of our reviews.”